Aluminum alloy die-casting heat treatment technology

Aluminum alloy die casting skills is to choose a standard heat treatment, heat treatment to control the heating rate rises to a corresponding temperature cooling, heat preservation time at a certain speed must change its alloy organization, its main purpose is to improve the mechanical properties of the aluminum alloy die casting, enhance the corrosion resistance, improve the processing performance, the stability of the standard. 

Skill characteristics 

Steels with a higher carbon content, after quenching, immediately acquire a high hardness and a low ductility.  But about aluminum alloy die casting, aluminum alloy die casting just after quenching, strength and hardness is not immediately increased, as for plasticity not only did not decline, but also increased.  But this quenched aluminum alloy die casting, placed for a period of time, the strength and hardness will be obvious if, and the plasticity is significantly reduced.  The phenomenon that the strength and hardness of aluminum alloy die casting after quenching increase obviously with time is called aging.  Aging can occur at room temperature, which is called natural aging, or it can occur at a temperature range higher than room temperature, which is called artificial aging. 

Aluminium alloy die casting 

Strengthening principle 

The aging hardening of aluminum alloy die casting is a proper and disorderly process, which not only depends on the composition and aging process of aluminum alloy die casting, but also depends on the defects formed in the production process of aluminum alloy die casting, especially the number and dispersion of vacancies and dislocations.  It is now generally believed that age hardening is the result of solute atom segregation to form a hardening region. 

When aluminum alloy die casting parts are quenched and heated, the vacancy is formed in the alloy. When quenching, because of the fast cooling, the vacancy is too late to be removed, and it is "fixed" in the crystal.  These vacancies in the over-full solid solution are mostly bound to solute atoms.  Because the over-full solid solution is in the unstable state, it is bound to change to the equilibrium state. The existence of vacancies accelerates the dispersion rate of solute atoms and thus accelerates the segregation of solute atoms. 

The size and number of hardening zones in aluminum alloy die castings depend on quenching temperature and quenching cooling rate.  The higher the quenching temperature is, the higher the vacancy concentration is, the more the number of hardening zones is, and the standard of hardening zone decreases.  The higher the quenching cooling rate is, the more vacancies are fixed in the solid solution, which is beneficial to add the number of hardening zone of aluminum alloy die casting and reduce the standard of hardening zone. 

One of the basic characteristics of the deposition hardened aluminum alloy die casting system is the equilibrium solid solubility that changes with temperature, that is, the solubility increases with the temperature, and most of the aluminum alloy die casting parts that can be heat treated to strengthen are in line with this condition.